The present invention relates to a power-saving control system for MCU (Micro Controller Unit) having a plurality of functional portions including a CPU (Central Processing Unit).
In order to reduce the size of a control circuit for controlling a hard disk or the like, an MCU has recently been developed as such a control circuit. The MCU is a one-chip device including a control portion, e.g., a CPU, and a peripheral portion, e.g., an A/D converter and a D/A converter. Many CPUs of such MCUs have a power-saving mode such as a sleep mode to reduce their electric power consumption while they are inactive. Once the power-saving mode is set in the CPU, the functional operation of the CPU is almost stopped. As a result, the overall functional operation of the MCU is stopped.
As described above, in the conventional system, when the power-saving mode is set in the CPU, the overall operation of the devices is stopped. Therefore, the operation of only a specific device cannot be stopped, and electric power is unnecessarily kept supplied to even devices in an inactive state. As a result, electric power is wasted. On the other hand, there has recently been increasing demand for reducing in the power consumption of the MCU even when the CPU is in operation.